Force sensing resistors are printed sensors that can detect the smallest amounts of force or pressure. Because of their extreme sensitivity, force sensing resistors can be used in countless applications in several industries, including inventory control, video games, robotics, and athletic apparel and sports equipment. 

"Use the Force, Luke"

Force sensing isn’t something a Jedi uses, as cool as that sounds. Printed force sensing resistors do precisely what their name implies—they sense forces. The “resistor” part of the name comes from the method it uses to sense the force: electrical resistance.  A force sensing resistor, or FSR for short, uses conductive silver and carbon inks printed between two layers of thin, flexible material. Think of it like a peanut butter and jelly sandwich. 

The sensor sends a small electrical current through each of the two surfaces.  When you press on the FSR pad, it makes a connection and gives a signal. The higher the force, the more the conductive inks smoosh together, and the electrical resistance lowers.

Force sensing resistors are versatile. They can be applied to many different applications and surfaces, including rigid and flexible surfaces.

Uses for Force Sensing Resistors

1. Athletic Apparel

A common application for force sensing resistors is athletic apparel, such as shoe insoles. Think of the Dr. Scholl's kiosks. A force sensing shoe insole will detect where the pressure of your foot is the greatest. This information can be used to design better running shoes. The data you get from the FSR insoles can help increase performance or prevent injuries. For example, the FSR can detect if somebody pronates when they run.  By monitoring the pressures, you can determine the changes needed to improve the shoes, and this helps athletes to run better.

2. Medical Applications

Force sensing resistors can sense forces as large as a human body or as light as a vial of medicine. FSRs can sense when pills are taken from a bottle to regulate medication use during a hospital stay. Another medical application would be for hospital beds. A doctor can determine if one area of the bed is receiving too much pressure, which could be an early indication of bed sores. This would alert the physicians that a patient needs to be moved or adjusted. Another potential medical application would be for bandages and wound care. A force sensing resistor could tell a physician or nurse that they’ve applied the right amount of pressure to a bandage.  It can also sense if a bandage becomes loose over time and can alert a medical practitioner to readjust the bandage.

3. Robotics

Applying a force sensing resistor on the end of a robotic arm gives real-time feedback to robots when they grab something or pick something up. It also could alert the robot how much pressure it puts on the object it picks up. This could be extremely useful when a robot has to pick up something fragile, like a 

4. Inventory Control 

Another common application for force sensing resistors is inventory control management. Force sensing resistors can be printed on a large sheet and attached to shelving units or wherever inventory is stored. As inventory is removed from the shelf, the amount of force applied changes, so a force sensing resistor can detect when inventory is running low. 

5. User Interface Controls

Force sensing resistors can act as non-tactile buttons. Using force sensing resistors as buttons makes the possibilities for programming multiple actions endless. Simply adjust the force of the resistor to elicit a range of actions, from light touches to more forceful pushes. This opens up a world of customization for user interface controls.

Combining Technologies for Innovative New Uses

The remarkable thing about this technology is that you can use it with additional technology. Other types of Advanced Printed Technology can be combined with force sensors. For example, FSRs can be combined with biometric sensors for a wound care bandage. Once the bandage has detected the correct amount of pressure has been applied, it can monitor for things like heartbeat, blood pressure, perspiration levels, and dehydration. When used with a printed heater, a force sensing resistor could help to keep objects warm when pressure is applied to it.

Force sensing resistors can even be integrated into today's technology and appliances. Picture a hair dryer that turns on when you squeeze the handle versus flipping a switch. How about a stove that turns on when you set the pot on the burner? Another innovative application could be FSR carpets in each of the rooms in your home. It would know when you’ve walked into a room and can turn on the lights, the radio or the television. It could even alert your Alexa or Google Home that you’re ready to communicate with it.

Pinpointing Touches: Where and How Much Pressure?

Force sensing resistors can give you resultant pressures and tell you precisely where a force is felt on their surface. A force sensing resistor can be designed to let you know the specific location of a touch or input. Imagine an entire wall as a force sensing resistor.  As you touch various areas of the wall, you get diverse feedback. In a classroom, for example, a world map painted on the wall embedded with FSRs could give audio or visual feedback as students interacted with the map. This could be a great hands-on learning tool to educate students about what’s going on in that part of the world, what countries they are touching, and more. The sky is the limit.

Start Your Project Today

We can see many force sensing applications from video games, medical applications, and sporting equipment. Force sensing resistors are a cool technology built for the future.

Can you think of new combinations for force sensing resistors?  Let us know your thoughts.